1. Field of the Invention
This invention relates to the measurement and identification of the relative time of arrival between two identical error free binary PN code sequences. The measurement technique is further extended to the measurement of the relative time of arrival between two identical binary PN code sequences having a limited number of errors.
2. Description of Prior Art
In the paper "Acquisition of Pseudonoise Signals by Recursion Aided Sequential Estimation," by R. B. Ward and K. P. Yiu, IEEE Transactions on Communications, Vol. COM-25, No. 1, August 1977, the authors present a technique for the acquisition of a known direct sequence spread spectrum (DSSS) signal based on sequential estimation. In the prior art of James C. Fletcher (U.S. Pat. No. 3,953,674), an advanced version of the recursion aided sequential estimator is utilized to rapidly acquire the proper PN code sequence generator state without slewing through all intervening states until the correct state (or code phase) is obtained. The techniques of Matthews (U.S. Pat. No. 3,728,533), Rauch (U.S. Pat. No. 3,774,206), and Ueda et al, (U.S. Pat. No. 5,128,961) slew the code phase for correlation using various techniques for the generation of the offset code phase. In the present invention, a parallel correlative technique is used to measure the code phase offset between two code sequences. In the case of DSSS signals, the receiver PN generator is already locked to the incoming signal and the binary code sequence from the receiver PN generator is correlated against a second reference sequence to identify the relative code phase offset between the two sequences.